He also talked about his opposition to gun control -- especially after voting against last week's effort to begin debate on the Democratic-backed Senate gun legislation. (The Senate voted, 68-31, to begin debate.)

On "Meet the Press," Rubio told NBC's David Gregory that he voted against the effort because he has concerns about any potential new gun law infringing on 2nd Amendment rights.

“I didn't write that into the Constitution,” he said. “That's in there. And any time that you're going to do anything that impacts a constitutional right, the scrutiny should be very, very high.”

“My skepticism about gun laws is that criminals don’t follow the law,” he said. “They don’t care what the law is. You can pass any law you want, criminals will ignore it.”

But that's a straw-man argument, gun-control advocates counter. Testifying in February before the Senate Subcommittee on the Constitution, Civil Rights, and Human Rights, Daniel Webster, the director of John Hopkins' gun policy center, contended that such logic would prevent laws against drunk driving -- because criminals don't follow the law.